Network Working Group D. Thaler
Request for Comments: 4903 Internet Architecture Board
Category: Informational June 2007
Multi-Link Subnet Issues
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
There have been several proposals around the notion that a subnet may
span multiple links connected by routers. This memo documents the
issues and potential problems that have been raised with such an
approach.
Table of Contents
1. Introduction ....................................................2
2. Issues ..........................................................3
2.1. IP Model ...................................................3
2.2. TTL/Hop Limit Issues .......................................4
2.3. Link-scoped Multicast and Broadcast ........................6
2.4. Duplicate Address Detection Issues .........................7
3. Security Considerations .........................................8
4. Recommendations .................................................9
4.1. IP Link Model ..............................................9
4.2. IPv6 Address Assignment ...................................10
4.3. Duplicate Address Detection Optimizations .................12
5. Normative References ...........................................12
6. Informative References .........................................13
Thaler Informational [Page 1]
RFC 4903 Multi-Link Subnet Issues June 2007
1. Introduction
The original IPv4 address definition [RFC791] consisted of a Network
field, identifying a network number, and a Local Address field,
identifying a host within that network. As organizations grew to
want many links within their network, their choices were (from
[RFC950]) to:
1. Acquire a distinct Internet network number for each cable;
subnets are not used at all.
2. Use a single network number for the entire organization, but
assign host numbers without regard to which LAN a host is on
("transparent subnets").
3. Use a single network number, and partition the host address
space by assigning subnet numbers to the LANs ("explicit
subnets").
[RFC925] was a proposal for option 2 that defined a specific type of
Address Resolution Protocol (ARP) proxy behavior, where the
forwarding plane had the properties of decrementing the Time To Live
(TTL) to prevent loops when forwarding, not forwarding packets
destined to 255.255.255.255, and supporting subnet broadcast by
requiring that the ARP-based bridge maintain a list of recent
broadcast packets. This approach was never standardized, although
[RFC1027] later documented an implementation of a subset of [RFC925].
Instead, the IETF standardized option 3 with [RFC950], whereby hosts
were required to learn a subnet mask, and this became the IPv4 model.
Over the recent past, there have been several newer protocols
proposing to extend the notion of a subnet to be able to span
multiple links, similar to [RFC925].
Early versions of the IPv6 scoped address architecture [SCOPID]
proposed a subnet scope above the link scope, to allow for multi-link
subnets. This notion was rejected by the WG due to the issues
discussed in this memo, and as a result the final version [RFC4007]
has no such notion.
There was also a proposal to define multi-link subnets [MLSR] for
IPv6. However, this notion was abandoned by the IPv6 WG due to the
issues discussed in this memo, and that proposal was replaced by a
different mechanism that preserves the notion that a subnet spans
only one link [RFC4389].
Thaler Informational [Page 2]
RFC 4903 Multi-Link Subnet Issues June 2007
However, other WGs continued to allow for this concept even though it
had been rejected in the IPv6 WG. Mobile IPv6 [RFC3775] allows
tunnels to mobile nodes to use the same subnet as a home link, with
the Home Agent doing layer 3 forwarding between them.
The notion also arises in Mobile Ad-hoc NETworks (MANETs) with
proposals that an entire MANET is a subnet, with routers doing layer
3 forwarding within it.
The use of multi-link subnets has also been considered by other
working groups, including NetLMM, 16ng, and Autoconf, and by other
external organizations such as WiMax.
In this memo, we document the issues raised in the IPv6 WG which
motivated the abandonment of the multi-link subnet concept, so that
designers of other protocols can (and should) be aware of the issues.
The key words "MUST", "RECOMMENDED", and "SHOULD" in this document
are to be interpreted as described in [RFC2119].
2. Issues
2.1. IP Model
The term "link" is generally used to refer to a topological area
bounded by routers that decrement the IPv4 TTL or IPv6 Hop Limit when
forwarding the packet. A link-local address prefix is defined in
both IPv4 [RFC3927] and IPv6 [RFC4291].
The term "subnet" is generally used to refer to a topological area
that uses the same address prefix, where that prefix is not further
subdivided except into individual addresses.
In December 1995, the original IP Version 6 Addressing Architecture
[RFC1884] was published, stating: "IPv6 continues the IPv4 model that
a subnet is associated with one link. Multiple subnets may be
assigned to the same link."
Thus, it explicitly acknowledges that the current IPv4 model has been
that a subnet is associated with one link and that IPv6 does not
change this model. Furthermore, a subnet is sometimes considered to
be only a subset of a link, when multiple subnets are assigned to the
same link.
The IPv6 addressing architecture has since been updated three times,
first in July 1998 [RFC2373], then April 2003 [RFC3513], and finally
in February 2006 [RFC4291]. All updates include the language:
"Currently IPv6 continues the IPv4 model that a subnet prefix is
Thaler Informational [Page 3]
RFC 4903 Multi-Link Subnet Issues June 2007
associated with one link. Multiple subnet prefixes may be assigned
to the same link."
Clearly, the notion of a multi-link subnet would be a change to the
existing IP model.
Similarly, the Mobility Related Terminology [RFC3753] defines a
Foreign subnet prefix as "a bit string that consists of some number
of initial bits of an IP address which identifies a node's foreign
link within the Internet topology" with a similar definition for a
Home subnet prefix. These both state that the subnet prefix
identifies a (singular) link.
2.2. TTL/Hop Limit Issues
Since a link is bounded by routers that decrement the IPv4 TTL or
IPv6 Hop Limit, there may be issues with applications and protocols
that make any assumption about the relationship between TTL/Hop Limit
and subnet prefix.
There are two main cases that may arise. Some applications and
protocols may send packets with a TTL/Hop Limit of 1. Other
applications and protocols may send packets with a TTL/Hop Limit of
255 and verify that the value is 255 on receipt. Both are ways of
limiting communication to within a single link, although the effects
of these two approaches are quite different. Setting TTL/Hop Limit
to 1 ensures that packets that are sent do not leave the link, but it
does not prevent an off-link attacker from sending a packet that can
reach the link. Checking that TTL/Hop Limit is 255 on receipt
prevents a receiver from accepting packets from an off-link sender,
but it doesn't prevent a sent packet from being forwarded off-link.
As for assumptions about the relationship between TTL/Hop Limit and
subnet, let's look at some example references familiar to many
protocol and application developers.
Stevens' "Unix Network Programming", 2nd ed. [UNP], states on page
490, "A TTL of 0 means node-local, 1 means link-local" (this of
course being true by the definition of link). Then page 498 states,
regarding IP_MULTICAST_TTL and IPV6_MULTICAST_HOPS, "If this is not
specified, both default to 1, which restricts the datagram to the
local subnet." Here, Unix programmers learn that TTL=1 packets are
restricted to a subnet (as opposed to a link). This is typical of
many documents that use the terms interchangeably due to the IP model
described earlier.
Thaler Informational [Page 4]
RFC 4903 Multi-Link Subnet Issues June 2007
Similarly, "TCP/IP Illustrated", Volume 1 [TCPILL], states on page
182: "By default, multicast datagrams are sent with a TTL of 1. This
restricts the datagram to the same subnet."
Steve Deering's original multicast README file [DEERING] contained
the statement "multicast datagrams with initial TTL 1 are restricted
to the same subnet", and similar statements now appear in many
vendors' documentation, including documentation for Windows (e.g.,
[TCPIP2K]) and Linux (e.g., [LINUX] says a TTL of 1 is "restricted to
the same subnet. Won't be forwarded by a router.")
The above are only some examples. There is no shortage of places
where application developers are being taught that a subnet is
confined to a single link, and so we must expect that arbitrary
applications may embed such assumptions.
Some examples of protocols today that are known to embed some
assumption about the relationship between TTL and subnet prefix are
the following:
o Neighbor Discovery (ND) [RFC2461] uses messages with Hop Limit
255 checked on receipt, to resolve the link-layer address of
any IP address in the subnet.
o Older clients of Apple's Bonjour [MDNS] use messages with TTL
255 checked on receipt, and only respond to queries from
addresses in the same subnet. (Note that multi-link subnets do
not necessarily break this, as this behavior is to constrain
communication to within a subnet, where a subnet is only a
subset of a link. However, it will not work across a multi-
link subnet.)
Some other examples of protocols today that are known to use a TTL 1
or 255, but do not appear to explicitly have any assumption about the
relationship to subnet prefixes (other than the well-known link-local
prefix) include the following:
o Link-Local Multicast Name Resolution [LLMNR] uses a TTL/Hop
Limit of 1 for TCP.
o Multicast Listener Discovery (MLD) [RFC3810] uses a Hop Limit
of 1.
o Reverse tunneling for Mobile IPv4 [RFC3024] uses TTL 255
checked on receipt for Registration Requests sent to foreign
agents.
Thaler Informational [Page 5]
RFC 4903 Multi-Link Subnet Issues June 2007
o [RFC3927] discusses the use of TTL=1 and TTL=255 within the
IPv4 link-local address prefix.
It is unknown whether any implementations of such protocols exist
that add such assumptions about the relationship to subnet prefixes
for other reasons.
2.3. Link-scoped Multicast and Broadcast
Because multicast routing is not ubiquitous, the notion of a subnet
that spans multiple links tends to result in cases where multicast
does not work across the subnet. Per [RFC2644], the default behavior
is that routers do not forward directed broadcast packets either, nor
do they forward limited broadcasts (see [RFC1812], Section 4.2.2.11).
There are many protocols and applications today that use link-scoped
multicast. The list of such applications and protocols that have
been assigned their own link-scoped multicast group address (and may
also have assumptions about the TTL/Hop Limit as noted above) can be
found at:
http://www.iana.org/assignments/multicast-addresses
http://www.iana.org/assignments/ipv6-multicast-addresses
In addition, an arbitrarily large number of other applications may be
using the all-1's broadcast address, or the all-hosts link-scoped
multicast address, rather than their own group address.
The well-known examples of protocols using link-scoped multicast or
broadcast generally fall into one of the following groups:
o Routing protocols: Distance Vector Multicast Routing Protocol
(DVMRP) [RFC1075], OSPF [RFC2328], RIP [RFC2453][RFC2080],
Enhanced Interior Gateway Routing Protocol (EIGRP) [EIGRP],
etc. These protocols exchange routes to subnet prefixes.
o Address management protocols: Neighbor Discovery, DHCPv4
[RFC2131], Dynamic Host Configuration Protocol for IPv6
(DHCPv6) [RFC3315], Teredo [RFC4380], etc. By their nature,
this group tends to embed assumptions about the relationship
between a link and a subnet prefix. For example, ND uses
link-scoped multicast to resolve the link-layer address of an
IP address in the same subnet prefix, and to do duplicate
address detection (see Section 2.4 below) within the subnet.
DHCP uses link-scoped multicast or broadcast to obtain an
address in the subnet. Teredo states that the Teredo IPv4
Discovery Address is "an IPv4 multicast address used to
Thaler Informational [Page 6]
RFC 4903 Multi-Link Subnet Issues June 2007
discover other Teredo clients on the same IPv4 subnet. The
value of this address is 224.0.0.253", which is a link-scoped
multicast address. It also says that "the client MUST silently
discard all local discovery bubbles [...] whose IPv4 source
address does not belong to the local IPv4 subnet".
o Service discovery protocols: Simple Service Discovery Protocol
(SSDP) [SSDP], Bonjour, WS-Discovery [WSDISC], etc. These
often do not define any explicit assumption about the
relationship to subnet prefix.
o Name resolution protocols: NetBios [RFC1001], Bonjour, LLMNR,
etc. Most often these do not define any explicit assumption
about the relationship to subnet prefix, but Bonjour only
responds to queries from addresses within the same subnet
prefix.
Note that protocols such as Bonjour and Teredo that drop packets that
don't come from an address within the subnet are not necessarily
broken by multi-link subnets, as this behavior is meant to constrain
the behavior to within a subnet, when a link is larger than a single
subnet.
However, regardless of whether any assumption about the relationship
to subnet prefixes exists, all protocols mentioned above or on the
IANA assignments lists will not work across a multi-link subnet
without protocol-specific proxying functionality in routers, and
adding proxying for an arbitrary number of protocols and applications
does not scale. Furthermore, it may hinder the development and use
of future protocols using link-scoped multicast.
2.4. Duplicate Address Detection Issues
Duplicate Address Detection (DAD) uses link-scoped multicast in IPv6
and link-scoped broadcast in IPv4 and so has the issues mentioned in
Section 2.3 above.
In addition, [RFC2462] contains the statement:
"Thus, for a set of addresses formed from the same interface
identifier, it is sufficient to check that the link-local address
generated from the identifier is unique on the link. In such
cases, the link-local address MUST be tested for uniqueness, and
if no duplicate address is detected, an implementation MAY choose
to skip Duplicate Address Detection for additional addresses
derived from the same interface identifier."
Thaler Informational [Page 7]
RFC 4903 Multi-Link Subnet Issues June 2007
The last possibility, sometimes referred to as Duplicate Interface
Identifier Detection (DIID), has been a matter of much debate, and
the current work in progress [2462BIS] states:
Each individual unicast address SHOULD be tested for uniqueness.
Note that there are implementations deployed that only perform
Duplicate Address Detection for the link-local address and skip
the test for the global address using the same interface
identifier as that of the link-local address. Whereas this
document does not invalidate such implementations, this kind of
"optimization" is NOT RECOMMENDED, and new implementations MUST
NOT do that optimization.
The existence of such implementations also causes problems with
multi-link subnets. Specifically, a link-local address is only valid
within a link, and hence is only tested for uniqueness within a
single link. If the same interface identifier is then assumed to be
unique across all links within a multi-link subnet, address conflicts
can occur.
3. Security Considerations
The notion of multi-link subnets can cause problems with any security
protocols that either rely on the assumption that a subnet only spans
a single link or can leave gaps in the security solution where
protocols are only defined for use on a single link.
Secure Neighbor Discovery (SEND) [RFC3971], in particular, is
currently only defined within a single link. If a subnet were to
span multiple links, SEND would not work as currently specified,
since it secures Neighbor Discovery messages that include link-layer
addresses, and if forwarded to other links, the link-layer address of
the sender will be different. This same problem also exists in cases
where a subnet does not span multiple links but where Neighbor
Discovery is proxied within a link. Section 9 of [RFC4389] discusses
some possible future directions in this regard.
Furthermore, as noted above some applications and protocols (ND,
Bonjour, Mobile IPv4, etc.) mitigate against off-link spoofing
attempts by requiring a TTL or Hop Limit of 255 on receipt. If this
restriction were removed, or if alternative protocols were used, then
off-link spoofing attempts would become easier, and some alternative
way to mitigate such attacks would be needed.
Thaler Informational [Page 8]
RFC 4903 Multi-Link Subnet Issues June 2007
4. Recommendations
4.1. IP Link Model
There are two models that do not have the issues pointed out in the
rest of the document.
The IAB recommends that protocol designers use one of the following
two models:
o Multi-access link model: In this model, there can be multiple
nodes on the same link, including zero or more routers. Data
packets sent to the IPv4 link-local broadcast address
(255.255.255.255) or to a link-local multicast address can be
received by all other interested nodes on the link. Two nodes
on the link are able to communicate without any IPv4 TTL or
IPv6 Hop Limit decrement. There can be any number of layer 2
devices (bridges, switches, access points, etc.) in the middle
of the link.
o Point-to-point link model: In this model, there are exactly two
nodes on the same link. Data packets sent to the IPv4 link-
local broadcast address or to a link-local multicast address
can be received by the other node on the link. The two nodes
are able to communicate without any IPv4 TTL or IPv6 Hop Limit
decrement. There can be any number of layer 2 devices
(bridges, switches, access points, etc.) in the middle of the
link.
A variant of the multi-access link model, which has fewer issues, but
still some, is the following:
o Non-broadcast multi-access (NBMA) model: Same as the multi-
access link model, except that no broadcast or multicast
packets can be sent, even between two nodes on the same link.
As a result, no protocols or applications that make use of
broadcast or multicast will work.
Links that appear as NBMA links at layer 3 are problematic. Instead,
if a link is an NBMA link at layer 2, then protocol designers should
define some mechanism such that it appears as either the multi-access
link model or point-to-point link model at layer 3.
One use of an NBMA link is when the link itself is intended as a
wide-area link (e.g., a tunnel such as 6to4 [RFC3056]) where none of
the groups of functionality in Section 2.3 are required across the
wide area. Admittedly, the definition of wide-area is somewhat
subjective. Support for multicast on a wide-area link would be
Thaler Informational [Page 9]
RFC 4903 Multi-Link Subnet Issues June 2007
analogous to supporting multicast routing across a series of local-
area links. The issues discussed in Section 2.3 will arise, but may
be acceptable over a wide area until multicast routing is also
supported.
Note that the distinction of whether or not a link is a tunnel is
orthogonal to the choice of model; there exist tunnel links for all
link models mentioned above.
A multi-link subnet model should be avoided. IETF working groups
using, or considering using, multi-link subnets today should
investigate moving to one of the other models. For example, the
Mobile IPv6 WG should investigate having the Home Agent not decrement
the Hop Limit, and forward multicast traffic.
When considering changing an existing multi-link subnet solution to
another model, the following issues should be considered:
Loop prevention: If physical loops cannot exist within the subnet,
then removing the TTL/Hop Limit decrement is not an issue.
Otherwise, protocol designers can (for example) retain the
decrement but use a separate prefix per link, or use some form of
bridging protocol instead (e.g., [BRIDGE] or [RBRIDGE]).
Limiting broadcast (including all-hosts multicast): If there is no
efficiency requirement to prevent broadcast from going to other
on-link hosts, then flooding it within the subnet is not an issue.
Otherwise, protocol designers can (for example) use a separate
prefix per link, or flood broadcast other than ARP within the
subnet (ARP is covered below in Section 4.3).
Limiting the scope of other multicast (including IPv6 Neighbor
Discovery): If there is no efficiency requirement to prevent
multicast from going to other on-link hosts, then flooding
multicast within the subnet is not an issue. Otherwise, protocol
designers can (for example) use a separate prefix per link, or use
Internet Group Management Protocol (IGMP)/MLD snooping [RFC4541]
instead.
4.2. IPv6 Address Assignment
In IPv6, the Prefix Information Option in a Router Advertisement (RA)
is defined for use by a router to advertise an on-link prefix. That
is, it indicates that a prefix is assigned to the link over which the
RA is sent/received. That is, the router and the node both have an
on-link route in their routing table (or on-link Prefix List, in the
conceptual model of a host in [RFC2461]), and any addresses used in
Thaler Informational [Page 10]
RFC 4903 Multi-Link Subnet Issues June 2007
the prefix are assigned to an interface (on any node) attached to
that.
In contrast, DHCPv6 Prefix Delegation (DHCP-PD) [RFC3633] is defined
for use by a client to request a prefix for use on a different link.
Section 12.1 of RFC 3633 states:
Upon the receipt of a valid Reply message, for each IA_PD the
requesting router assigns a subnet from each of the delegated
prefixes to each of the links to which the associated interfaces
are attached, with the following exception: the requesting router
MUST NOT assign any delegated prefixes or subnets from the
delegated prefix(es) to the link through which it received the
DHCP message from the delegating router.
Hence, the upstream router has a route in its routing table that is
not on-link, but points to the client; the prefix is assigned to a
link other than the one over which DHCP-PD was done; and any
addresses used in the prefix are assigned to an interface (on any
node) attached to that other link.
The IAB believes that the distinction between these two cases
(assigning a prefix to the same link vs. another link) is important,
and that the IETF protocols noted above are appropriate for the two
scenarios noted. The IAB recommends that other protocol designers
remain consistent with the IETF-defined scopes of these protocols
(e.g., not using DHCP-PD to assign a prefix to the same link, or
using RAs to assign a prefix to another link).
In addition, the Prefix Information Option contains an L (on-link)
flag. Normally, this flag is set, indicating that this prefix can be
used for on-link determination. When not set, the advertisement
makes no statement about on-link or off-link properties of the
prefix. For instance, the prefix might be used for address
configuration with some of the addresses belonging to the prefix
being on-link and others being off-link. Care must be taken when the
L flag is not set. Specifically, some platforms allow applications
to retrieve the prefix length associated with each address of the
node. If an implementation were to return the prefix length used for
address configuration, then applications may incorrectly assume that
TTL=1 is sufficient for communication, and that link-scoped multicast
will reach other addresses in the prefix. As a result, the IAB
recommends that designers and maintainers of APIs that provide a
prefix length to applications address this issue. For example, they
might indicate that no prefix length exists when the prefix is not
on-link. If the API is not capable of reporting that one does not
exist, then they might choose to report a value of 128 when the
prefix is not on-link. This would result in such applications
Thaler Informational [Page 11]
RFC 4903 Multi-Link Subnet Issues June 2007
believing they are on separate subnets, rather than on a multi-link
subnet.
4.3. Duplicate Address Detection Optimizations
One of the reasons sometimes cited for wanting a multi-link subnet
model (rather than a multi-access link model), is to minimize the
ARP/ND traffic between end-nodes. This is primarily a concern in
IPv4 where ARP results in a broadcast that would be seen by all
nodes, not just the node with the IPv4 address being resolved. Even
if this is a significant concern, the use of a multi-link subnet
model is not necessary. The point-to-point link model is one way to
avoid this issue entirely.
In the multi-access link model, IPv6 ND traffic can be reduced by
using well-known multicast learning techniques (e.g., [RFC4541] at a
layer 2 intermediate device (bridge, switch, access point, etc.).
Some have suggested that a layer 2 device could maintain an ARP or ND
cache and service requests from that cache. However, such a cache
prevents any type of fast mobility between layer 2 ports, and breaks
Secure Neighbor Discovery [RFC3971]. As a result, the IAB recommends
to protocol designers that this approach be avoided, instead using an
alternative such as layer 2 learning. For IPv4 (where no Secure ARP
exists), the IAB recommends that protocol designers avoid having a
device respond from its cache in cases where a node can legitimately
move between layer 2 segments of the link without any layer 2
indications at the layer 2 intermediate device. Also, since
currently there is no guarantee that any device other than the end-
host knows all addresses of the end-host, protocol designers should
avoid any dependency on such an assumption. For example, when no
cache entry for a given request is found, protocol designers may
specify that a node broadcast the request to all nodes.
5. Normative References
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC950] Mogul, J. and J. Postel, "Internet Standard Subnetting
Procedure", STD 5, RFC 950, August 1985.
[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Thaler Informational [Page 12]
RFC 4903 Multi-Link Subnet Issues June 2007
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2644] Senie, D., "Changing the Default for Directed Broadcasts in
Routers", BCP 34, RFC 2644, August 1999.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and B.
Zill, "IPv6 Scoped Address Architecture", RFC 4007, March
2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, May 2006.
6. Informative References
[2462BIS] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", Work in Progress, May 2005.
[BRIDGE] T. Jeffree, editor, "Media Access Control (MAC) Bridges",
ANSI/IEEE Std 802.1D, 2004, http://standards.ieee.org/
getieee802/download/802.1D-2004.pdf.
[DEERING] Deering, S., "IP Multicast Extensions for 4.3BSD UNIX and
related systems (MULTICAST 1.2 Release)", June 1989.
http://www.kohala.com/start/mcast.api.txt
Thaler Informational [Page 13]
RFC 4903 Multi-Link Subnet Issues June 2007
[EIGRP] Cisco, "Enhanced Interior Gateway Routing Protocol", Cisco
Document ID 16406, September 2005.
http://www.cisco.com/warp/public/103/eigrp-toc.html
[LINUX] Juan-Mariano de Goyeneche, "Multicast over TCP/IP HOWTO",
March 1998. http://www.linux.com/howtos/Multicast-HOWTO-
2.shtml
[LLMNR] Aboba, B., Thaler, D., and L. Esibov, "Link-local Multicast
Name Resolution (LLMNR)", RFC 4795, January 2007.
[MDNS] Cheshire, S. and M. Krochmal, "Multicast DNS", June 2005.
http://files.multicastdns.org/draft-cheshire-dnsext-
multicastdns.txt
[MLSR] Thaler, D. and C. Huitema, "Multi-link Subnet Support in
IPv6", Proceedings of IETF 54, June 2002.
http://www.ietf.org/proceedings/02jul/I-D/draft-ietf-ipv6-
multilink-subnets-00.txt
[RBRIDGE] Perlman, R., Gai, S., and D. Dutt, "Rbridges: Base Protocol
Specification", Work in Progress, March 2007.
[RFC925] Postel, J., "Multi-LAN address resolution", RFC 925,
October 1984.
[RFC1001] NetBIOS Working Group in the Defense Advanced Research
Projects Agency, Internet Activities Board, and End-to-End
Services Task Force, "Protocol Standard for a NetBIOS
Service on a TCP/UDP Transport: Concepts and Methods", STD
19, RFC 1001, March 1987.
[RFC1027] Carl-Mitchell, S. and J. Quarterman, "Using ARP to
Implement Transparent Subnet Gateways", RFC 1027, October
1987.
[RFC1075] Waitzman, D., Partridge, C., and S. Deering, "Distance
Vector Multicast Routing Protocol", RFC 1075, November
1988.
[RFC1884] Hinden, R., Ed., and S. Deering, Ed., "IP Version 6
Addressing Architecture", RFC 1884, December 1995.
[RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
January 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
Thaler Informational [Page 14]
RFC 4903 Multi-Link Subnet Issues June 2007
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453, November
1998.
[RFC3024] Montenegro, G., Ed., "Reverse Tunneling for Mobile IP,
revised", RFC 3024, January 2001.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[RFC3753] Manner, J., Ed., and M. Kojo, Ed., "Mobility Related
Terminology", RFC 3753, June 2004.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3810] Vida, R., Ed., and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380, February
2006.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[SCOPID] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., Onoe,
A., and B. Zill, "IPv6 Scoped Address Architecture",
Proceedings of IETF 54, July 2002.
http://www.ietf.org/proceedings/02jul/I-D/draft-ietf-
ipngwg-scoping-arch-04.txt
[SSDP] Goland, Yaron Y., Cai, T., Leach, P., Gu, Y., and S.
Albright, "Simple Service Discovery Protocol (SSDP)", 1999.
http://www.upnp.org/resources/specifications.asp
Thaler Informational [Page 15]
RFC 4903 Multi-Link Subnet Issues June 2007
[TCPILL] Stevens, W. Richard, "TCP/IP Illustrated, Volume 1",
Addison-Wesley, 1994.
[TCPIP2K] MacDonald, D. and W. Barkley, "Microsoft Windows 2000
TCP/IP Implementation Details". http://www.microsoft.com/
technet/itsolutions/network/deploy/depovg/tcpip2k.mspx
[UNP] Stevens, W. Richard, "Unix Network Programming, Volume 1,
Second Edition", Prentice Hall, 1998.
[WSDISC] Microsoft, "Web Services Dynamic Discovery (WS-Discovery)",
2005. http://specs.xmlsoap.org/ws/2005/04/discovery/ws-
discovery.pdf
IAB Members at the time of this writing
Bernard Aboba
Loa Andersson
Brian Carpenter
Leslie Daigle
Elwyn Davies
Kevin Fall
Olaf Kolkman
Kurtis Lindqvist
David Meyer
David Oran
Eric Rescorla
Dave Thaler
Lixia Zhang
Author's Address
Dave Thaler
Microsoft
One Microsoft Way
Redmond, WA 98052
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com
Thaler Informational [Page 16]
RFC 4903 Multi-Link Subnet Issues June 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Thaler Informational [Page 17]